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ransactions of the Royal Society of Tropical Medicine and Hygiene (2009) 103, 390—394

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istribution trends of Salmonella serovarsn India (2001—2005)

ashwant Kumar ∗, Anshu Sharma, Rakesh Sehgal, Sunil Kumar

ational Salmonella and Escherichia Centre, Central Research Institute,asauli — 173204, Himachal Pradesh, India

eceived 5 April 2008; received in revised form 12 September 2008; accepted 12 September 2008vailable online 23 October 2008

KEYWORDSSalmonella;Distribution;Biotyping;Serotyping;Serovars;India

Summary A total of 3079 samples were received and identified at the National Salmonellaand Escherichia Centre (NSEC), Central Research Institute, Kasauli, India during 2001—2005.Out of these, 2098 samples were from humans, 250 from animals, and 726 from meat, veg-etables, seafood and the environment. The Salmonella strains isolated were distributed among35 different Salmonella serovars. The most common serovars from humans were SalmonellaTyphi (73%) and Salmonella Paratyphi A (24%) among typhoidal serovars, and Salmonella Wor-thington (28.2%) and Salmonella Typhimurium (22.5%) among non-typhoidal serovars. The otherfrequently isolated serovars from different sources were Salmonella Gallinarum, Salmonella

Typhimurium, Salmonella Enteritidis and Salmonella Dublin. Analysis of the prevalence of the10 most common serovars in 18 states indicated that different serovars are distributed in dif-ferent parts of India. The results from this study may be helpful in formulating preventivestrategies to control the spread of infection in the country.

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© 2008 Royal Society of Trreserved.

. Introduction

almonellae are primarily intestinal parasites of humans andany animal species including domestic pets, wild birds,

odents and other wild animals. The environmental distri-ution of salmonellae is evident from their isolation from

ewage, rivers and other waterbodies, and soil in which theyemain somewhat dormant.1 Infection of domestic animalsith various serovars of Salmonella sometimes results in

erious illness causing tremendous economic losses2 as well

∗ Corresponding author. Tel.: +91 1792 272060x218.E-mail address: yasht26@yahoo.co.in (Y. Kumar).

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035-9203/$ — see front matter © 2008 Royal Society of Tropical Medicinoi:10.1016/j.trstmh.2008.09.009

l Medicine and Hygiene. Published by Elsevier Ltd. All rights

s being a reservoir for the disease in humans.3 Salmonellas one of the most common causes of enteric infections inumans and is associated with significant morbidity and mor-ality, especially in developing countries.4

Infections are associated primarily with unhygienic con-itions, and improper handling and cooking of food items.

large number of food and animal sources have beeneported to act as reservoirs of salmonellae.5 More than500 serovars of Salmonella have been identified in different

6

arts of the world and most of them have been describeds causative agents of human disease. The reported num-er of cases is lower than the actual incidence rate dueo frequent under-reporting. The most common causes ofuman salmonellosis have been reported to be the serovars

e and Hygiene. Published by Elsevier Ltd. All rights reserved.

Distribution of Salmonella serovars in India 391

Table 1 Annual distribution of typhoidal and non-typhoidal Salmonella serovars (2001—2005).

Serovar Year Total

2001 2002 2003 2004 2005

TyphoidalS. Typhi 320 214 198 124 57 913S. Paratyphi A 41 120 65 81 13 320S. Paratyphi B 4 1 11 16 14 46S. Paratyphi C — — 5 — — 5Total 365 335 279 221 84 1284

Non-typhoidalS. Typhimurium 105 124 36 84 95 444S. Worthington 133 73 21 32 32 291S. Enteritidis 56 89 90 18 5 258S. Dublin — — 27 114 59 200S. Bareilly 4 27 29 14 50 124S. Weltevreden 29 20 26 32 27 134S. Gallinarum 47 39 15 11 6 118S. Infantis 28 39 12 9 11 99

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Other 34 9Total 436 420

a Details of all non-typhoidal serovars are given in Supplementary

Typhimurium and Enteritidis, which account for 57—67% oftotal annual isolates5; however, some regions are dominatedby other serovars.7

Epidemiological data such as geographical distribution,source distribution and time distribution are of immenseimportance in tracing and dealing with new emergingpathogens. The global importance of the distribution ofdifferent Salmonella serovars lies in the travelling of peo-ple and the trade in food and animals. Epidemiologicalstudies describe the trends in prevalence of human andanimal salmonellosis. Methods exploiting phenotypic char-acteristics such as biotype and serotype have provideduseful epidemiological markers for primary discriminationof Salmonella serovars.

The National Salmonella and Escherichia Centre (NSEC),Central Research Institute, Kasauli, India, has provided aservice to the nation for the past five decades, analysingdifferent isolates of Salmonella and Escherichia. This Cen-tre is a national reference laboratory and was previouslyunder the control of WHO. It receives a sufficient numberof samples from different research laboratories, hospitalsand institutions all over the country to accurately assess thenational distribution of Salmonella serovars.

During 2001—2005 the NSEC received samples from 39hospitals, 14 research institutes, five laboratories of thefisheries and food departments, 9 clinical laboratories and32 agricultural and veterinary institutes. The samples weretested for antigenic identity based on biotyping and serotyp-ing, and the data was analysed to indicate the prevalence ofdifferent serovars in different regions of the country amonghuman and animal species.

2. Methods and materials

Bacterial isolates submitted to the NSEC for serologicalidentification were analysed. Ready-made media and bio-

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17 35 32 127273 349 317 1795

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hemicals (Hi Media Lab. Pvt. Ltd., Mumbai, India) wererocured in their dehydrated form. Other chemicals usedere of analytical grade (Merck Ltd., Mumbai, India). Glass-istilled water was used for preparation of media andeagents.

Different O and H antisera (Central Research Institute,asauli, India; Seiken Laboratories, Tokyo, Japan) were used

n the present study for serotyping of the isolates.Isolates submitted to NSEC under specified conditions

ere checked for any breakage and leakage of the container.orphological characteristics and motility were observed byram staining and hanging drop preparation respectively.atalase and oxidase tests were performed by the stan-ard procedures. Individual isolates were then biotyped,sing a range of biochemical tests.8 Isolates suggestive ofalmonella were further subjected to serotyping.6

. Results

ut of 4672 isolates submitted for analysis, 3079 were iden-ified as Salmonella. Among the total of 35 serovars, the 10ost common were Salmonella Typhi (29.7%) and Salmonella

aratyphi A (10.4%) among typhoidal salmonellae, andalmonella Typhimurium (24.7%), Salmonella Worthington16.2), Salmonella Enteritidis (14.4%), Salmonella Dublin11.1%), Salmonella Weltevreden (7.5%), Salmonella Bareilly6.9%), Salmonella Gallinarum (6.5%) and Salmonella Infan-is (5.3%) among non-typhoidal isolates (Table 1). Of thether 25 serovars, two were typhoidal Salmonella serovarsTable 1) and 23 were non-typhoidal Salmonella serovarsSupplementary Table 1).

During the study period, the commonest typhoidalalmonellae was Salmonella Typhi (71.1%) and the least fre-uent was Salmonella Paratyphi C (0.39%) (Table 1). Theatio of Salmonella Typhi:Salmonella Paratyphi A isolatesas 7.8, 1.8, 3, 1.5 and 4.4 in 2001, 2002, 2003, 2004

392

Table 2 Invasive index of non-typhoidal Salmonellaserovars in India (2001—2005).

Non-typhoidalserovar

No. of isolationsfrom blood

Total no. ofisolations

Invasiveindexa

S. Worthington 87 239 0.364S. Typhimurium 59 191 0.309S. Enteritidis 29 71 0.41S. Bareilly 12 88 0.136S. Senftenberg 2 4 0.5S. Weltervreden 9 93 0.097S. Infantis 16 68 0.24S. Poona 6 10 0.6S. Derby 4 16 0.25

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S. Newport 1 27 0.04S. Virchow 1 2 0.5a Invasive index = blood isolations/total isolations.

nd 2005 respectively. In non-typhoidal salmonellae theroportions of different isolates ranged from 24.7% to 0.05%ith Salmonella Typhimurium (Table 1) being the com-onest. The invasive index of 11 non-typhoidal Salmonella

erovars ranged from 0.6 to 0.04 (Table 2).It should be noted that samples from different hospitals,

esearch institutions and laboratories were not collectedtrictly in accordance with the protocol required for anypidemiological study. The complete array of reservoirs hasot been included in the study. The present data are basedn only a few reservoirs for which samples had been sub-itted to the NSEC for serotyping. These reservoirs mainly

ncluded poultry, human, meat, environment, vegetables,

nimals and seafood (Table 3; Supplementary Table 2).

Among typhoidal salmonellae the largest proportion ofsolates was from humans (97.4%) with the smallest fromnimals (0.08%) and meat (0.08%) (Table 3). For non-yphoidal salmonellae also, the largest proportion of isolates

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Table 3 Distribution of typhoidal and non-typhoidal Salmonella s

Serovar Poultry Human Meat

TyphoidalS. Typhi 2 911 —S. Paratyphi A 19 300 1S. Paratyphi B 11 35 —S. Paratyphi C — 4 —Total 32 1250 1

Non-typhoidalS. Typhimurium 184 191 4S. Worthington 21 239 —S. Enteritidis 174 71 —S. Dublin — 8 —S. Bareilly 28 88 —S. Weltevreden 11 93 —S. Gallinarum 102 8 1S. Infantis 17 68 8Othera 20 82 1Total 557 848 14

a Details of all non-typhoidal serovars are given in Supplementary Tabl

Y. Kumar et al.

47.2%) was from humans. Distribution among other reser-oirs showed 31%, 13.9%, 3.9%, 1.9%, 1.2% and 0.2% fromoultry, animals, seafoods, vegetables, environment andeat respectively (Table 3; Supplementary Table 2). Anal-

sis of the prevalence of the 10 most common serovars in8 states indicated that different serovars are distributed inifferent parts of India (Supplementary Table 3).

. Discussion

n the present study, the commonest of the typhoidalerovars was found to be Salmonella Typhi, showing itsndemic nature in the country.9 A substantial increase inalmonella Paratyphi A has been reported in India sinceate 1990s and antimicrobial resistance has also increased.10

oreover, several reports have been published recentlyeporting a high incidence of Salmonella Paratyphi A infec-ion as compared to Salmonella Typhi.11—13 In the presenttudy, the ratio of isolations of Salmonella Typhi:Salmonellaaratyphi A was found to be highest in the year 2004.his raises an important issue of the need for a safe andotent vaccine against Salmonella Paratyphi A in India. Ancetone-killed and dried vaccine (comprising Salmonellayphi, Salmonella Paratyphi A and Salmonella Paratyphi B)s being produced in India, but it is not easily available and isot free from adverse effects. For all the typhoidal serovarshe largest proportion of isolates were from humans, show-ng their host specificity. The small number of isolationsrom other reservoirs suggested they may have a role inransmission. The isolation of Salmonella Paratyphi A (6%)nd Salmonella Paratyphi B (24%) from poultry is significantTable 3). Isolation of human Salmonella serovars from poul-

ry shows that these animals may present a public healthazard by spreading this infection to humans directly or viaheir eggs.

Salmonella Typhimurium is one of the commonesterovars isolated in India.9 Unsurprisingly, it was found to

erovars among different reservoirs (2001—2005).

Environment Vegetables Animals Seafood

— — — —— — — —— — — —— — 1 —0 0 1 0

5 28 23 912 1 — 181 — 3 9— 5 187 —— — 1 71 — 16 133 — — 4— 1 2 3— — 17 7

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Distribution of Salmonella serovars in India

be the most common serovar among non-typhoidal serovars(Table 1) isolated from all the reservoirs (Table 3) inthe present study. This shows it can survive in differenttypes of reservoirs which may act as sources of infec-tion to humans.14 Furthermore, Salmonella Typhimuriumshowed a high frequency in poultry (41.4%) and humans(43%) (Table 3). This suggests the possible transmission ofSalmonella Typhimurium from poultry to humans. Moreover,this serovar is widely distributed among all the reservoirsunder study showing its easy transmissibility to humansthrough different sources.

Salmonella Worthington has been reported from differentparts of the world from cases of diarrhoea15 and infan-tile gastroenteritis.16,17 It is commonly isolated in India andis implicated in outbreaks of meningitis, septicaemia anddiarrhoea.18—20 Salmonella Worthington has also been iso-lated from various systemic complications.21,22 In our study,the number of isolates of Salmonella Worthington receivedwas the second highest among non-typhoidal Salmonellaisolates. The increasing number of isolates of SalmonellaWorthington and its high invasive index (Table 2) raisesstrong concerns about the frequency of systemic infectionsdue to this serovar in the country. Salmonella Worthingtonisolated from almost every reservoir except meat and ani-mals showing its wide distribution in nature. It is the mostcommon serovar being isolated from seafood, and is gainingimportance as a cause of invasive as well as non-invasiveinfections in different age groups. Therefore, more studieson this serovar are required pertaining to its potential tocause severe systemic infection.

Salmonella Enteritidis, Salmonella Gallinarum andSalmonella Infantis are the serovars having poultry as themain reservoir.23—25 Salmonella Enteritidis and SalmonellaInfantis were also isolated from humans signifying the pos-sibility of transmission of infection from poultry productsto them. Moreover, they have been isolated from blood(Table 2) showing their invasive nature.

Salmonella Weltevreden was found to be of zoonotic sig-nificance in India and has been constantly recorded and isone of the five serovars isolated most frequently.26 It is alsoisolated from blood showing its possible involvement in sys-temic infections (Table 2). It was isolated from seafoods,and therefore, undercooked seafood may possibly transmitits infection.

The potential of Salmonella serovars to cause invasivediseases has been reported.27 In our study the invasiveindex of non-typhoidal salmonellae ranged from 0.6 to 0.04among 11 non-typhoidal salmonellae (Table 3) showing thepredilection of non-typhoidal salmonellae to cause systemicinfections and therefore several medical complications.Therefore steps should be taken to stop the transmissionof these serovars in addition to typhoidal serovars.

Areas of the world with ample opportunities for fae-cal contamination of water and food continue to have highrates of enteric infections. The present study shows thatSalmonella serovars are widely distributed in different partsof India with differences in distribution of different serovars

among different geographic areas. Almost all the serovars(10 most common serovars) were found to be present inDelhi, Tamil Nadu, Maharashtra and Kerala (SupplementaryTable 3). This may be due to the presence of metropolitancities in first three states and the popularity of Kerala for

393

ourism. There is a large influx of people into these statesn search of work as they are industrial hubs. They mayake different Salmonella serovars along with them fromheir native places. Salmonella Worthington was found toe present in northern, central and southern parts of Indiaut not in eastern and western areas. It was found to beresent in eight states among 18 under study. The numberf isolations was found to be highest in Maharashtra fol-owed by Delhi and Tamil Nadu. Salmonella Typhi was foundo be present in almost every region. The geographic distri-ution is likely to be related to the available reservoirs forersistence and spread of salmonellae infections.

In brief, it is concluded that the government should takeecessary steps to further strengthen the surveillance pro-rammes to limit the high rate of morbidity and mortalitymong the population due to salmonellae infections. Suchrogrammes would not only reduce mortality and morbid-ty but would also lower the economic burden and lead to aealthy nation.

uthors’ contributions: YK and AS conceived and designedhe study; YK did the serotyping assisted by SK; YK and SKompiled the data; RS and AS analysed and interpreted theata. All authors participated in the preparation and revisionf the manuscript and read and approved the final version.K and RS are guarantors of the paper.

cknowledgements: The authors thank the heads of all theaboratories that referred Salmonella isolates to this centre.he technical assistance of Mr Prem and Mr Jagdish Kumar

s also acknowledged. Thanks are due to Mr Jiwa Ram forupplying media and biochemicals for biotyping.

unding: None.

onflicts of interest: None declared.

thical approval: Not required.

ppendix A. Supplementary data

upplementary data associated with this article can beound, in the online version, at doi:10.1016/j.trstmh.008.09.009.

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